The present invention relates to a one-component RTV silicone rubber composition and more particularly the present invention relates to self-bonding silyl ether functional one-component RTV silicone rubber compositions.
One-component RTV (RTV stands for room temperature vulcanizable) silicone rubber compositions have been known for some time. The earlier compositions comprised as the basic ingredients a silanol terminated polymer which was reacted with an acetoxy-functional silane to produce a linear polymer having acetoxy-functional terminal groups. The resulting polymer would cross-link in the presence of atmospheric moisture to produce a silicone elastomer at room temperature. Complete cure occurred in a rather rapid fashion, that is, in from 24 to 72 hours when there was also present a curing promoter which was preferably a metal salt of a carboxylic acid. The salt was desirably a tin salt of a carboxylic acid. The composition is called a one-component composition since all the ingredients are mixed together in a single package and when it is desired to apply the composition, the seal on the package is broken, the composition is applied to whatever form desired and it crosslinks upon exposure to atmospheric moisture to a silicone elastomer.
There are other types of RTV's with different types of functionality; see, for example, U.S. Pat. No. 4,100,129. It was desirable to discover various types of one-component RTV's with different functionalities so as to have the desired properties in the RTV system. Thus, the alkoxy-functional RTV has advantageous properties in that it is relatively non-corrosive and does not have any objectionable odor contrary to the properties of the acetoxy-functional RTV's. However, the alkoxy-functional RTV's do not cure at a sufficient rate even with various types of curing promoters such as titanium esters.
Accordingly, one attempt to resolve this problem was the discovery of silyl ether-functional RTV's. See for instance, U.S. Pat. Nos. 4,176,111, 4,176,112, 4,223,122, and 4,238,401 which are exemplary of such systems and which disclosures are hereby incorporated by reference. U.S. Pat. No. 4,176,111 disclosed the basic dimedone or silyl ether-functional RTV system. However, the basic system cured at too rapid a rate and accordingly in order to give the composition some work life before curing, it was recommended in the above patent that there be a high carbon alkyl radical attached to the silicon atom to which the silyl ether-functional group was appended. It was found that such a higher alkyl radical on the terminal silicone atoms slowed the cure of the system through stearic hindrance. A still further solution that was proposed was the utilization of an alkoxy group on the silicon atom to which the silyl ether group was appended thereto. While these modifications operated with varying success, it was found that such silyl ether functional compositions suffer from a basic deficiency; that is, they did not have good adhesion to various substrates. It should be noted that other types of functional RTV systems also did not have superior adhesion to substrates. Therefore, there were incorporated into such RTV compositions, various types of self-bonding additives so as to make the composition have superior self-bonding properties to substrates without the use of a primer. Thus, for instance, see the use of the acyloxy, alkoxy-functional silanes of Kulpa U.S. Pat. No. 3,296,161 and Gossens, U.S. Pat. No. 3,296,195 which resulted in superior adhesion of the acetoxy-functional RTV systems to various types of substrates. Also, the enhancement of the self-bonding properties of an alkoxy-functional RTV system by the use of silyl isocyanurate self-bonding additives is disclosed in U.S. Pat. No. 4,100,129. There can also be noted the use of silyl maleates, silyl fumarates, and the like as self-bonding additives in acyloxy-functional and alkoxy-functional RTV's as disclosed in Mitchell et al, U.S. Pat. No. 4,273,698 which is hereby incorporated by reference. However, these self-bonding additives which perform in a superior manner for the the acyloxy functional and alkoxy functional RTV systems, were not found to work as well with the silyl ether functional system. In this respect, it should be noted that the diacyloxy, dialkoxy silane of Kulpa U.S. Pat. No. 3,296,161, was not tested in the silyl ether functional RTV system since it liberates a corrosive acid, that is, acetic acid. Accordingly, for this reason, it would be undesirable in the dimedone or silyl ether-functional RTV system.
Accordingly, it was highly desirable to find a self-bonding additive for dimedone or silyl ether-functional RTV systems.
Accordingly, it is one object of the present invention to provide for a self-bonding additive for a dimedone or silyl ether-functional RTV system.
It is yet an additional object of the present invention to provide a process for forming self-bonding dimedone-functional one-component RTV systems.
It is still an additional object of the present invention to provide a self-bonding dimedone-functional RTV system that has good self-bonding properties to metallic substrates.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.